Merge Conflicts

Our last merge went rather smoothly, but not all merges do. Let's demonstrate what a merge conflict looks like and how we can resolve it.

Conflict Prep

Let's start a new branch called swiss, cause I like a bit of swiss with my ham sandwich. But don't switch to that branch just yet.

$ git branch swiss

But, I also like cheddar on my ham sandwiches. I'm gonna edit the text to say cheddar, under cheese. Remember, I'm still on the master branch making this change.

*bread*
*meat*
ham
*cheese*
cheddar
*veggies*
onions
*bread*

Then lets add and commit it.

$ git add sandwich.txt
$ git commit -m "adding some cheddar"

If you check the log, you'll see that swiss (and ham) is one commit behind master now.

$ git log --decorate

Ready Conflict

Now lets switch into swiss.

$ git checkout swiss

As we saw in master, swiss doesn't know about the cheddar related commit. Let's just confirm that with a git log.

$ git log --decorate

Nope, no cheddar there.

Since we're in the swiss branch, let's go ahead and add the swiss to our sandwich.txt. I'm also gonna add some lettuce.

*bread*
*meat*
ham
*cheese*
swiss
*veggies*
onions
lettuce
*bread*

And then add and commit.

$ git add sandwich.txt
$ git commit -m "i prefer swiss"

What do you think will happen when we try to merge it into master?

Conflict!

Switch to master, then try to merge in swiss.

$ git checkout master
$ git merge swiss

Git encountered a conflict while trying to automatically merge our sandwich.txt. Git also left us some helpful clues in sandwich.txt, to help us figure where the conflict happened.

Open up sandwich.txt to see what notations git has added to the file.

This may seem a bit intimidating at first glance, but it can be super helpful.

First, lets note the format:

<<<<<<< <current_location_name>
<current_text>
=======
<merging_in_text>
>>>>>>> <mergin_in_location>

We can see that HEAD, which is our current spot on master added "cheddar". And the top part shows us that.

Then after the =======, we see that "swiss" came in from the branch we were merging in, swiss.

Ok, so, how do we fix it?

Cleaning up a Conflict

First, pick which is correct, "cheddar" or "swiss". Then remove the incorrect line, and the lines that git added (prefixed by <<<<<<, ========, >>>>>>).

I'm gonna pick "cheddar", because if I'm honest, I'm not actually a fan of holey cheese.

To resolve my conflict with "cheddar", I'm gonna remove the "swiss" line, and the git lines.

You'll notice this looks a lot like our original cheddar commit, except that this one includes the "lettuce" we also added in our swiss branch.

Now if we do a git status we can see how we finish this merge conflict.

Git tells us that, after we've fixed the conflict (which we did above), we need to git add that file.

$ git add
$ git status

To conclude the merge, we need to do a git commit.

git commit -m "Merge branch 'swiss'"

We have resolved the conflict!

Another way to resolve the conflict would have been to choose both cheeses for our sandwich. The conflict could have been resolved by having one, the other, or both lines chosen to resolve the conflict.